Recently, in view of improving the fuel consumption and cleaning the exhaust gas of automobiles, development of injectors capable of more precisely controlling the fuel injection is demanded. As for such a highly precise injector, use of a stacked piezoelectric element as the actuator has been proposed. However, a stacked piezoelectric element having excellent durability and applicable to the actuator of those injectors has not yet been put into practice at present.
The stacked piezoelectric element can be produced, for example, by printing and forming an inner electrode layer of 5 μm on a green sheet having a thickness of about 100 μm, stacking, for example, hundreds of such green sheets, subjecting the stacked green sheets to press-molding, drying, firing, machining and the like to form a stacked body, and joining a side electrode to a side face of the stacked body.
For improving the durability of the stacked piezoelectric element, the inner electrode layer exposed to the side face of the stacked body must be insulated, without fail, so as to prevent the generation of migration or the like.
Japanese Unexamined Patent Publication (Kokai) No. 5-160458 discloses a method of applying an insulating resin coat to the inner electrode exposed to the side face of a stacked body and thereby preventing the migration of silver. However, this method has a problem in that if the resin coat is stripped off, water or the like intrudes to cause migration of silver and insulation failures.
As for the method of insulating the inner electrode layer exposed to the outer peripheral side face of a stacked body, Japanese Unexamined Patent Publication (Kokai) No. 2001-244514 has proposed a method of machining grooves and filling a resin in each groove to achieve insulation by resin. However, it is not practicable, in mass production, to machine grooves having a depth of 500 μm and a height (width) of 50 μm by a cutting saw as disclosed in this patent document.
For example, as described in Patent Publication No. 2001-244514, when grooves are provided on the side face of a stacked body, the insulating resin filled in the groove is stably maintained by an anchor effect and the durability can be improved.
However, machining of grooves by a cutting saw is industrially difficult in view of the working efficiency and, also, the stacked body may be damaged during the machining to cause a problem in quality.
The present invention has been made for solving these problems in conventional techniques and an object of the present invention is to provide a method for producing a stacked piezoelectric element, where grooves can be easily formed on the side face of a stacked body without causing damage.